The present invention relates to a thermoplastic olefin elastomer (abbreviated as TPO hereinafter), and more particularly, it relates to a TPO suitable for use as an injection molding material for automotive exterior trim such as side molding, bumper, and mud guard.
TPO has come to find use as a raw material for automotive exterior trim because of its low specific gravity, good low temperature resistance, and good weatherability. Recently, the automotive exterior trim is required to have a matte-finished appearance. Unfortunately, trim of matte-finished uniform appearance cannot be made from a conventional TPO by injection molding, because the resulting molded item has flow marks (or swirl marks) attributable to the rubber component (EPDM) contained therein.
Flow marks can be eliminated and injection molding with a good matte-finished appearance can be obtained if the rubber component in TPO is partly crosslinked. (See Japanese Patent Laid-open Nos. 18943/1972, 26838/1973, 145847/1978, 142753/1977, and 1386/1979. ) The partial crosslinking process requires a difficult control in the production of TPO injection molding materials. Thus, TPO of stable quality is difficult to produce and, as the result, the TPO injection molding material is expensive.
In the meantime, the abbreviations used in this specification are defined as follows:
TPO: Thermoplastic olefin elastomer PA0 EPDM: Ethylene-propylene-diene terpolymer PA0 EVA: Ethylene-vinyl acetate copolymer PA0 PP: Polypropylene PA0 Mn: Number-average molecular weight PA0 wt%: Weight percentage